A wireless X-ray detector for a digital radiography system with remote detection of impinging radiation from the system X-ray source onto a sensor panel having amorphous or crystalline silicon photodiodes or metal insulated semiconductor (MIS) sensors. Changes in current in the photodiode bias supply circuit is sensed to generate a signal indicating presence of radiation. Improved detection of X-ray cessation is achieved either by leaving at least one line of sensors connected between the bias supply circuit to a virtual ground during charge accumulation or by using an X-ray presence detector circuit that increases the sensitivity of the detector circuit to bias circuit current changes occurring after onset of the radiation.